This invention relates to a cathode ray tube and more particular, to an envelope for a cathode ray tube of a multinecks structure.
Color cathode ray tubes for large-sized, high brightness, high resolution color TV receives for use in high definition TV systems, or for large-sized, high resolution graphic display units for use in computer terminals, demand specification requirements differing from those for color cathode ray tubes applicable to general consumer applications. Various investigations have been carried out to satisfy these specification requirements.
A high brightness and a high resolution shadow mask color cathode ray tube with a small-sized screen are at present commercially available. However, the tube with a large-sized screen having a sufficient high degree of brightness and resolution have not been commercially realized. The main reason for this shortcoming can be attributed to the increase in the magnification factor of the electron-optics of the electron gun which would necessarily accompany any extend tube depth due to possible increases in tube dimensions. There is a reduction in the electron beam energy intensity on the screen surface as a result of any screen enlargement.
In order to settle such drawback, a color cathode ray tube of a multinecks structure with a high resolution and brightness has been proposed in U.S. Pat. Nos. 4,712,038, 4,714,856 and 4,792,720. The multinecks color cathode tube is illustrated in FIG. 1 showing a cross-sectional view of the tube. In the tube 1, a vacuum envelope 2 includes a panel 3 composed of a single faceplate 4 with a rectangular inner surface and a skirt 5 extending parallel to a central axis Z from a periphery of the faceplate 4, a funnel 6 hermetically connected to the skirt 5 at its end and a plurality of necks 7a, 7b, 7c and 7d. In each necks 7a, 7b, 7c and 7d, each electron gun assemblies 8a, 8b, 8c and 8d is provided for emitting three electron beams 9a, 9b, 9c and 9d. In the drawing, three electron beams are illustrated by a single line for simplification, respectively. A phosphor screen 10 is formed on the inner surface of the faceplate 4 for reproducing color image by exitation of the electron beams 9a, 9b, 9c and 9d. A mask 11 with a plurality of apertures allowing a passage of the electron beams is provided in the panel 3 by support of a mask frame 12 so as to have predetermined distance between the phosphor screen 10 and the mask 11.
During an operation of the tube mentioned above, the electron beams 9a, 9b, 9c and 9d are deflected by deflection yoke 13a, 13b, 13c and 13d so as to scan the first, second third and fourth regions 10a, 10b, 10c and 10d of the phosphor screen 10, respectively.
As seen from FIG. 1, since the envelope 2, especially, the funnel 6 has a complex configuration, it is difficult for forming it, and consequently, the envelope 2 is not suitable for mass production. Namely, it is necessary to have a circular openings 14a, 14b, 14c and 14d for hermetically connecting to the necks 8a, 8b, 8c and 8d, respectively. In addition, walls 15a, 15b, 15c, 15d and 15e, which confine the respective opening 14a, 14b, 14c and 14d, should be inclined so as to allow the passage of the electron beams 9a, 9b, 9c and 9d from the electron gun assemblies 8a, 8b, 8c and 8d toward the phosphor screen 10, respectively. Further, it is difficult to correctly and hermetically connect the necks 7a, 7b, 7c and 7d to the walls 15a, 15b, 15c, 15d and 15e of the funnel 6 at the openings 14a, 14b, 14c and 14d, respectively, in order that the electron beams correctly land the phosphor screen region.
Furthermore, as the size of the envelope 2 is increased, it is necessary to make glass thickness of the funnel 6 almost as thick as glass thickness of the panel 3 in order to maintain the strength against atmospheric pressure. On the other hand, the necks 7a, 7b, 7c and 7d, which are hermetically connected to the funnel 6, is made of glass of which thickness is normally very thin at about 1 mm. The heat distribution from the funnel 6 to the necks 7a, 7b, 7c changes abruptly. Consequently, the heat strain in the multiple heating processes which are undergone during the manufacturing process of the tube increases and the envelope tends to be broken at the connection between the neck and the funnel. Therefore, the envelope with the construction mentioned above is unsuitable for mass-production.
As an envelope for a flat panel display device. U.S. Pat. No. 4,325,489 discloses the envelope which is suitable for production of the display device. The envelope comprises a baseplate and a faceplate held in a spaced parallel relationship by a plurality of sidewalls and a plurality of support walls formed by vanes and vane tips. The support walls support he baseplate and faceplate against atmospheric pressure and divide the envelope into a plurality of longitudinally extending channels. The envelope also includes a flexible seal with a space which accomondates for dimensional difference between the sidewalls and support walls.
The flexible seal is composed of a pair of continous members which are fritted to the faceplate of glass and the sidewalls of metal, respectively. Since the members are flexible and deformed without rupturing the weld along a seam of the members, stress in the frits due to different thermal expansion coefficient can be minimized.
The larger the screen size of the cathode ray tube, the more difference of thermal expansion amount between the faceplate and the sidewalls. Since the flexible seal is not sufficient for compensation of the increased difference of the thermal expansion amount in the case of the tube with the large screen, cracks will occure at frit sealing portion.